Controlling emissions of highly ozone-depleting agents has been recognized as a global challenge since the opening for signature of the Montreal Protocol in 1987. Ten years later, a similar challenge was also introduced against emissions of greenhouse gases by the ratification of the Kyoto Protocol. Since then, emissions of ozone-depleting agents have been mainly reduced by limiting the use of chlorofluorocarbons as refrigerants, while current efforts of controlling emissions of greenhouse gases are mainly focused on CO2 capture and storage processes. In this scenario, the currently uncontrolled and globally increasing atmospheric release of halogenated anaesthetics might end up becoming a dangerously underestimated opponent. Indeed, such compounds have the same ozone-depleting potential of chlorofluorocarbons plus a global warming potential much higher than that of carbon dioxide. In some countries, such as Canada, some healthcare settings have already adopted conventional anaesthetic capture systems, which typically work by means of adsorption processes. Such conventional approaches may need improvements and a higher global diffusion in order to make the adsorption of emitted anaesthetics as efficient as possible. Increased efficiency may be achieved by developing new adsorbent materials with very high adsorption capacity towards emitted anaesthetics and ease of regeneration.
Since at least 1975, more public attention has been directed to addressing the potential damage that the release of halogenated general anaesthetic gases constitutes for the global environment. Almost all the species that are currently employed as volatile anaesthetics (namely, desflurane, enflurane, halothane, isoflurane and sevoflurane) are halogenated organic compounds potentially noxious to the ozone layer. As modern anaesthesia becomes more and more available to the world population, the global usage of volatile anaesthetics is quickly growing. Anaesthetic vapours are also extensively employed in dentistry, veterinary medicine and research activities involving animals for in vivo experiments. What distinguishes these anaesthetic vapours from other medical drugs is that very small amounts are metabolized with excess emitted into the outside environment. Conventionally, most anaesthesia systems directly discharge the excess gaseous mixtures into the atmosphere, without any specific treatment. Whereas the installation of scavenging systems may decrease spillage of general anaesthetics into operating rooms, they are often still freely vented into the environment. Moreover, scarce attention has been paid to the ecotoxicological properties of gaseous general anaesthetics.
From a chemical point of view, halogenated volatile anaesthetics are in the same category of chlorofluorocarbons (CFCs), that constitute the class of the most aggressive ozone depleting agents. Moreover, the global warming potential (GWP) of halogenated anaesthetics is generally considered to be three orders of magnitude higher than that of carbon dioxide.
Halogenated ethers, such as sevoflurane, are successfully used as anesthetics. During an operation, only a small amount of the administered anesthetic (generally less than 5%) is metabolized by the patient. The remaining approximately 95% either escapes or is vented through hospital ventilation systems unabated directly into the atmosphere (M. Eic, “Proposal for collaboration,” Fredericton, NB, 2013).
In order to prevent the release of halogenated ethers into the environment, there has been a focus on developing adsorbents that can selectively remove and recover halogenated anesthetics from an exhaust gas stream. The adsorbents are specialized because of the need to remove the halogenated eithers at low concentration and in relatively humid air (for example, in some cases, 1% v/v sevoflurane with 50% relative humidity).
It would be desirable, thus, to provide an improved anaesthetic adsorbent that provides improved characteristics over conventional adsorbents.